Sounds like you found the problem.

I would go one step further and take that ground cable connection off and make sure it is a clean connection. Then put it back on and tighten it up.
If it is the one I think it is it probably has some rust or corrosion on the nut/washer. I replaced mine with a stainless washer and nylon lock nut so it won't corrode again nor come loose again.
It was Metric as I recall.

Good detective work...

Silverfox

 

Chances are (Johnny Mathis reference) the ground strap was arcing. Better check for burned places.

 

Then tie a yellow ribbon round that old Oak tree!!
Ok agreed no more Tony Orlando

 

So far, so good...no clicks yesterday..

 

Good to go!!

 

Gee, oldblue, no Johnny Mathis comments?

Yesterday I was in a truck shop. I had delivered a rebuilt starter the day before. The rebuilt starter is sitting on the workbench next to a ground strap that is green in the braid and melted on the block end, and a brand new ground strap.

H'mmm, I wonder if they really needed that $600 starter.

 

I just wear a funny grin!! I get misty!

 

It's good to go, no more clicks. The loose ground near the battery was the problem.
How it got loose to begin with is another question as it has a lock nut on the bottom and had some resistance while i was tightening it. Weird.